Terminal device for absorbing electromagnetic energy



o. E. Kir-:Now 2,567,379

TERMINAL DEVICE FOR ABSORBING ELECTROMAGNETIC ENERGY Filed July 20, 1944 sept, 1 1, 1951 Patented Sept. 11, 1951 TERMINAL DEVICE FOR ABSORBING ELECTROMAGNETIC ENERGY Orwald E. Kienow, South Acton, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application July 20, 1944, Serial No. 545,839

3 Claims. (Cl. 178-44) This invention relates to a means for terminating a coaxial transmission line, a hollow wave guide or other pieces of high frequency electrical equipment in an infinite line.

In the development and testing of ultra high frequency equipment it is frequently desired to provide a terminal device which may be readily connected to the element under test and which will provide a termination for the same having the characteristics of an infinite line.

It is among the objects of the invention to provide a terminal device such that when looking into the device from the piece of electrical equipment under test the impedance will be equivalent to the impedance of an infinite line.

It is a further object of the invention to provide a. method for manufacturing such terminal devices.

A further object of the invention is to provide a terminal device which may be readily assembled in conjunction with 'the electrical apparatus tested.

The above and other objects and Vfeatures of the invention will be fully apparent to those skilled in the art from a consideration of the following detailed description taken in conjunction with the accompanying drawing in which:

Fig. 1 represents a longitudinal section through a terminal device of the coaxial line type constructed in accordance with the invention;

Fig. 2 shows, on a reduced scale, a detail of a portion of the device shown in Fig. 1 in the process of manufacture;

Fig. 3 represents a longitudinal section through another form of the terminal device constructed -in accordance with the invention and suitable for v.use in conjunction with hollow wave guides; and

Fig. 4 is a section taken on line 4-4 of Fig. 3.

Referring to the drawing, and iirst to Figs. 1 and 2 thereof, there is shown a coaxial line comprising an outer conductor 2 and an inner coaxial conductor 3. The outer conductor is preferably constructed of a plurality of sections comprising end sections 4 and 5 which may be of copper tubing or other conductive material, and a central support section 6 also of conductive material. The outer end of the section 4 is closed by end plug 1 and the outer end of section 5 is end section 4 by a machine screw IIlextending 2 through the end plug 1 and coacting with an internally threaded bore in the end of the section 9. The opposite end of the section 9 is connected to a support section I I by a suitable socket connection. The central support section 6, which for the sake of rigidity may be of thicker material than the end sections 4 and 5, includes a stub support I2 Which in the instance shown is a lquarter wave stub line. However, it will be understood that the support for the inner coaxial conductor at this point may be of the same type as that shown in the copending application of Joseph Goldsmith, Serial No. 522,489, led February 15, 1944. Preferably the coaxial conductor 3 is provided with a transformer I3 comprising an enlargement thereof extending for a quarter Wave length on each side of the axis of the stub support I2 for the purpose of cancelling any reiiections due to the support. In order to terminate the device in a line, which looking in the direction of the end plug 1 will appear to be of innite length and accordingly have no redections, I provide a covering on the section 9 of the coaxial line, which covering gradually increases inv diameter toward the end plug 1 until the covering completely iills the space between the inner conductor and the outer conductor 4. The covering must be of a material which is a good absorber of high frequency Waves and I have found that a material impregnated with a rubber compound high in carbon black is ideal for this purpose. Preferably the material impregnated is cotton cloth and the impregnating compound is suciently high in carbon black to provide conduction paths of high resistance between adjacent particles. Low concentrations of carbon black so fully dispersed in rubber that there can be no conduction between adjacent particles are not suitable for the purposes of the present in'- vention.

In the manufacture of the device the impregnated cloth I4 is cut in the form of a triangle 'having one side of approximately the same length as the length of the section 9 of the coaxial conductor. The triangular strip is attached to the section 9 along this side thereof and. the section 9 is rotated so that the cloth is Wound upon this section. As the cloth is wound on the section 9, successive layers of the cloth build up a continuously increasing thickness of impregnated material in the direction of the long side of the trianglar strip I4. Thus as shown at the right hand end of the section 9 there is but one layer of the impregnated material, the number of layers successively increasing toward the left until, when where the internal diameter of the outer conductor is about 0.811 inch and the diameter of the inner conductor is about0.3'75 inch, if the length of the section 9 is about 13 inches, a sufcient taper in the covering of the materialis provided.

Under these conditions the length of the side of the triangular strip attached to the section 9v will be approximately 13 inches and the length of this strip, taken on the long side of the triangle, will be approximately 44 inches. With these dimensions the covering at the end of the section adjacent the long side of the strip will be suflicient-to ll the coaxial conductor 4 with a sliding fitv at the large end of the section 9.

In operation it will be understood that the device vis adapted to be attached at the flanged end 8 to a piece of electrical equipment to be tested. If the piece of electrical equipment includes a coaxial conductor the inner conductor 3 is connected to the centralY conductor of the apparatus by a suitable socket connection-or if the equipment to be testedterminates in a hollow cylindrical guide the inner conductor 3 may be terminated therein by a suitable exciting rod. When so positioned, the device, as seen looking from the equipment under test in the direction of the end plug 1, provides an impedance equivalent to an infinite line.

Referring to the form shown in Figs. 3 and 4, reference numeral 2l indicates a section of a hollow rectangular wave guide having one end closed by an end plug 22 and having a ange 2 3 at the opposite end for connecting the device to a piece of electrical equipment to be tested. In this form of the invention an innite impedance,

as seen looking into the guide 2| toward the end plug 22', is provided by means of a block 24 forming a pyramidal or cone shaped structure gradually tapering from the end of the guide adjacent the flange 23 toward the end plug 22. Adjacent the plug 22 the block 24 has a rectangular base portion 25 dimensioned to fitA tightly within this end of the wave guide 2|. The structure 24 is preferably made of non-conductive material such as well seasoned wood and is preferably divided into two sections 26 and 21. Each of these sections 26 and 2l is separately covered on all of the surfaces thereof with a material 28 which is a good absorber of Ihigh frequency waves such as the cloth I4 described in the form of the invention shown in Figs. 1 and 2. In the form of the invention shown in Figs. 3 and 4, however, the tapering structure is not built up of the absorbent material but constitutes an absorbent screen covering, the non-conductive material forming the tapered block 24 and also forming a partition separating the two sections 26 and 21 of the block.

The form of the terminal device shown in these figures is adapted to be connected to some piece of electrical equipment having a rectangular Wave guide and when so connected provides the equivalent of an infinite line looking in the direction of the end plug 22. Waves passing in the direction of the end plug are absorbed by the covering 28, which covering is so kgradually tapered that reflections therefrom are avoided. Any wave energy not absorbed by the covering on the outer or exposed surface of the block is absorbed by the absorbing material between the two sections 26 and 21. The structure thus prevents any reflections of the waves from the piece of -equipmentnnder test.

' While there has herein been described illustrative embodiments of the invention, other embodiments within the scope of the appended claims will be apparent to those skilled in the `artmfro'rn the, disclosure hereof and the teachings herein. For example, it will be evident that the invention can be readily applied to wave guides of types having a diferent geometry from the rectangular form shown in Figs. 3 and 4.

Likewise if desired the block 24 may be divided into a larger number of sections instead of two as shown and such division in some instances as in cylindrical guides is especially desirable.

lZVlfiatis claimed is: Y 1. A terminal device for a guided wave system comprising: a Atransmission line section includ: ing coaxially disposed inner and outerconductors; a Yplug closing. one end of. said. outer conductor; means passing through. said plug and engaging the' adjacent end of said inner conductor, for supporting said end of said inner con.- ductor in spaced relationship to said outer. conductor; means, adjacent the other Yend ofsaid outer conductor and engaging, said inner-.conductor along the length thereof, for similarly supporting the-other end of said innerconductor; and alaminarly-wrapped covering of a material which is highlyv absorbent of electromagnetic energy, about said inner conductor said covering filling .the space between said innerand outer conductors at the end adjacent said plug-'and tapering substantially linearlyalong sai-d -inner conductor toward the opposite end of saidsection. 2. -A terminal device for a guided Wave system comprising: a transmission line section including coaxially disposed inner and outer conductors; a plug closing-one end of said outer conductor; means passingr through said plu-g and engaging the adjacent end of said inner-"conductor, for supporting saidA end of saidw inner conductor -in spaced relationship to said outer conductor; means, adjacent the otherend of said outer conductor and engaging said inner conductor along the length thereof, for similarly supporting Vthe other end. ofsaid inner conductor; and-.a covering, consisting of cloth impregnated with a material which is highly absorbent of electromagneticenergy, wrapped. about said inner conductor;l said covering filling the space between said inner and outer conductors at the. end adjacent said plug and tapering substantially. linearly along said inner conductor toward the opposite end of said. section.

3. .A terminal device for a guided wave system comprising: a transmissionline section including coaxiallydisposed inner and outer conductors.; a plug closing one end of,v said outer conductor; means passing through said plug and engaging the adjacent end of said inner conductor,- for supporting said end of said inner. conductor in spaced relationship to said outer conductor; means, adjacent the other end of said outer conductor-and engaging said inner conductor along thelength thereof, for similarly supporting the other, end of said inner conductor; and a covering, consisting of cloth impregnated with a m-aterial, con.- taining carbon black in, a form ,which is highly absorbent of electromagnetic energy, wrapped about said inner conductor; said covering filling the space between said inner and outer conductors at the end adjacent said plug and tapering substantially linearly along said inner conductor toward the opposite end of said section.

ORWALD E. KIENOW.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Number Name Date Von Radinger 1 Feb. 17, 1942 Latimer May 7, 1946 Tiley Oct. 15, 1946 Korman July 1, 1947 Linder Nov. 4, 1947 Gunter Jan. 13, 1948 Feenberg May 31, 1949 FOREIGN PATENTS Country Date Germany July 22, 1930 

